1. Field of the Invention
The present invention relates to a semiconductor device capable of supplying a drive voltage to a high-side drive circuit by means of a bootstrap capacitor while a high-side drive circuit is performing negative-bias drive.
2. Background Art
In a half-bridge circuit, a drive voltage higher than the voltage of a main power supply is required for a high-side drive circuit for driving a high-side switching element. Also, with drive of a low-side switching element, a reference potential (a potential at a low-voltage terminal) for the high-side drive circuit fluctuates between a high-voltage-side potential and a low-voltage-side potential in the half-bridge circuit. There is, therefore, a need to use a floating power supply floating from the low-voltage-side potential as a drive voltage source for the high-side drive circuit. Obtaining a voltage for driving the high-side drive circuit by charging a bootstrap capacitor connected between a high-voltage terminal and a low-voltage terminal of the high-side drive circuit from a low-side drive power supply is known (see, for example, Japanese Patent Laid-Open No. 11-205112).
In a semiconductor device using a bootstrap circuit, a low-voltage terminal of a high-side drive circuit is connected to a connection point between a high-side switching element and a low-side switching element. Therefore, when the potential at the low-voltage terminal of the high-side drive circuit is made equal to GND potential by turn-on of the low-side switching element, a bootstrap capacitor is charged.
A semiconductor device is also known in which a high-side drive circuit performs negative bias drive. This semiconductor device has a reference voltage circuit that generates a reference voltage between the voltage at a high-voltage terminal of the high-side drive circuit and the voltage at a low-voltage terminal of the high-side drive circuit and supplies the reference voltage to the source of a high-side switching element. The high-side drive circuit is thereby enabled to supply a negative voltage to the gate of the high-side switching element with respect to the source at the time of turn-off.